Mauna Kea is the highest volcano on the Island of Hawai‘i and one of the most distinctive volcanic landscapes in the Hawaiian Islands. Rising to 13,803 feet above sea level, the volcano is now in an advanced postshield stage, with long periods of quiet separating relatively infrequent eruptions. Its most recent eruptions occurred roughly 6,000 to 4,000 years ago, but geologic evidence shows that Mauna Kea is likely to erupt again.
A future Mauna Kea eruption would probably look different from the frequent, relatively fluid lava eruptions associated with younger Hawaiian volcanoes. Mauna Kea’s past postshield eruptions produced lava flows, cinder cones, and tephra, with its more viscous lava creating thick and rubbly flows across parts of the upper slopes. A new eruption could therefore build another cinder cone while sending lava downslope from one or more vents.
The location of a future vent would be especially important. Lava flowing from a high-elevation vent could follow the steep and irregular slopes of Mauna Kea, potentially covering roads, infrastructure, and parts of the surrounding landscape. The exact direction and distance would depend on where the eruption occurred, the amount of lava produced, and the terrain the flow encountered.
Mauna Kea also has an unusual relationship with snow and ice. The summit has experienced repeated glaciation during past ice ages, and it is the only Hawaiian volcano known to have been glaciated. Although a future eruption would not necessarily produce a major water-related hazard, the presence of snow or ice could influence how eruptive heat interacts with the summit environment.
Explosive activity is another possibility. Mauna Kea’s geologic record contains substantial tephra deposits associated with past eruptions, showing that its activity has not always been limited to quiet lava effusion. A future eruption could therefore produce ash and other volcanic fragments in addition to lava, although the exact style and size of the eruption would be impossible to predict in advance.
So, what would happen if Mauna Kea erupted? The main hazards could include lava flows, cinder-cone formation, tephra and ashfall, volcanic gases, and localized impacts on roads and infrastructure. The effects would depend heavily on the location of the new vent, the amount and type of magma involved, the steepness of the terrain, and the conditions on the mountain at the time of the eruption.
Table of Contents
Before the Eruption: Earthquakes, Ground Deformation, and Other Warning Signs
A future eruption of Mauna Kea would likely be preceded by changes in the volcano’s behavior that scientists could detect through monitoring. Because Mauna Kea has been quiet for thousands of years, scientists would pay close attention to earthquake activity, ground deformation, and other changes that could indicate movement of magma or fluids beneath the volcano.
Earthquakes would be one of the most important warning signs. As magma or volcanic fluids move through cracks beneath a volcano, they can generate earthquakes as surrounding rock responds to changing pressure. Scientists would look for changes in the number, depth, location, and pattern of earthquakes rather than treating an individual earthquake as evidence that an eruption was about to begin.
A sustained earthquake swarm beneath Mauna Kea could be more significant. USGS notes that a swarm could signal that an eruption might occur within a relatively short period, although earthquake swarms do not always lead to an eruption. This distinction would be important because Mauna Kea also experiences earthquakes that are unrelated to magma movement.
Ground deformation could provide another important clue. If magma began accumulating or moving beneath the volcano, parts of Mauna Kea could slowly expand or tilt. GPS instruments and other geodetic measurements could detect subtle changes in the shape or elevation of the volcano.
Scientists would also compare several monitoring signals rather than relying on one measurement. Increasing seismicity combined with measurable ground deformation would provide stronger evidence of volcanic unrest than either signal alone. Changes in other observations could also help determine whether the activity represented normal background behavior or a developing volcanic process.
The location and depth of earthquakes would be particularly important. Recent earthquake activity beneath the broader Mauna Kea region has included events that were attributed to the underlying Kohala volcano rather than magma moving beneath Mauna Kea itself. This illustrates why scientists must carefully distinguish ordinary or tectonic earthquakes from signals that could indicate renewed activity at Mauna Kea.
Even a period of increased unrest would not guarantee an eruption. Volcanic systems can become more active without ultimately producing an eruption, and scientists would need to evaluate how multiple monitoring signals changed over time.
If several indicators began changing together, however, scientists could potentially recognize that Mauna Kea was moving toward an eruptive phase. The exact timing, vent location, and size of a future eruption would still be difficult to predict, but monitoring could provide valuable warning before magma reached the surface.
This early warning would be particularly important because Mauna Kea’s next eruption could occur from a vent on its upper flanks rather than at one fixed summit location. Understanding where magma was moving and how the volcano was responding would help scientists assess which areas could eventually face lava flows, tephra, and other volcanic hazards.
What Would Happen When Mauna Kea Became Active?
If Mauna Kea began showing sustained signs of volcanic unrest, scientists would closely monitor the volcano for evidence that magma was moving toward the surface. Increasing earthquakes, ground deformation, and other changes could indicate that the volcanic system was becoming more active, although such signals would not necessarily mean that an eruption was certain.
If magma continued rising, activity could eventually progress toward the opening of a new vent. Unlike a volcano with one permanently active crater, Mauna Kea has produced eruptions from multiple vents across its summit and upper flanks. The location of a future vent would therefore be one of the most important factors in determining how the eruption developed and which areas could be affected.
A new eruption could begin relatively quietly before becoming more vigorous. Magma reaching the surface could produce lava, volcanic gases, fragments of volcanic rock, and tephra. Because Mauna Kea is in an advanced postshield stage, its magma is generally more viscous than the very fluid lava associated with the volcano during its earlier shield-building stage. This has contributed to the formation of thicker lava flows and prominent cinder cones during its later eruptions.
The eruption could also produce a new cinder cone if explosive bursts of gas and magma fragmented volcanic material around the vent. Mauna Kea’s upper slopes are already dotted with numerous cinder cones formed during past eruptions, so a future eruption could add another volcanic feature to the mountain.
The surrounding terrain would then become increasingly important. Mauna Kea has relatively steep and irregular upper slopes compared with younger shield-stage volcanoes such as Mauna Loa. As eruptive material accumulated or lava moved away from a new vent, the shape and slope of the terrain would influence where volcanic material traveled.
Snow and ice could also interact with an eruption if activity occurred during a period when snow covered the summit. Heat from lava or other eruptive material could melt snow and ice locally, while the interaction between hot volcanic material and water could influence the behavior of some eruptive deposits. The exact effects would depend on the location and intensity of the eruption.
The eruption would not necessarily remain constant. Mauna Kea’s postshield eruptions have occurred as relatively infrequent and sporadic episodes rather than as the sustained, high-output activity characteristic of some younger Hawaiian volcanoes. A future eruption could therefore be relatively short-lived, although the duration and intensity could not be known in advance.
Once magma reached the surface, the main question would become where the volcanic material would go. Lava could move downslope, while tephra and ash could be carried by the wind. The location of the vent, the amount of magma erupted, the shape of the terrain, and weather conditions would determine the geographic extent of the hazards.
For that reason, a Mauna Kea eruption would not necessarily produce one uniform pattern of damage. The effects could range from localized volcanic activity near a new vent to lava flows and tephra affecting much larger areas of the mountain and surrounding landscape. The next major concern would be how far lava from a future vent could travel and which parts of the island could potentially be affected.
Could Mauna Kea Produce Lava Flows, and How Far Could They Travel?
Yes. Lava flows would be one of the most likely hazards from a future Mauna Kea eruption. USGS assessments indicate that the next eruption will probably produce a lava flow because every eruption during the past 60,000 years has produced lava flows. The same eruptive history suggests that a future eruption could also construct a new cinder cone around the vent.
The location of the new vent would be one of the most important factors controlling where the lava traveled. Mauna Kea has produced eruptions from multiple vents across its summit and upper flanks rather than from one permanently fixed opening. Lava emerging from a high-elevation vent could therefore move in a different direction from lava produced elsewhere on the volcano.
Mauna Kea’s postshield-stage lava is generally more viscous than the extremely fluid basalt associated with the volcano during its earlier shield-building stage. Past postshield eruptions produced many thick, rubbly ʻāʻā lava flows, although more fluid pāhoehoe could form close to some vents. These differences would affect how quickly lava moved and how far it could eventually spread.
The steep and irregular topography of Mauna Kea would also influence the flow. Lava would tend to move downslope under gravity, following the underlying terrain and spreading into areas where the slope became gentler. A flow could divide into multiple lobes as it encountered changes in elevation and surface features.
Past eruptions provide some indication of the potential reach. USGS-related assessments estimate that the longest future lava flows could travel about 9 to 15 miles downslope, although most future flows would be shorter. The actual distance would depend on the volume and temperature of the lava, the location of the vent, the slope of the terrain, and how quickly the lava cooled and solidified.
A future lava flow would not necessarily move rapidly across the landscape. Hawaiian lava flows generally advance downslope, but their speed can vary substantially depending on lava type, slope, eruption rate, and whether channels or lava tubes develop. A slower-moving flow could still cause extensive damage by covering roads, structures, and other infrastructure in its path.
The direction of a future flow would therefore be impossible to determine before the location of the eruptive vent was known. A vent on one part of Mauna Kea could send lava toward a completely different area from a vent elsewhere on the mountain. This is why lava-flow hazard assessments consider both the locations of past vents and the terrain surrounding the volcano.
The effects would also depend on how much lava was erupted. A small eruption could produce a relatively short flow confined to the upper slopes, while a larger eruption could send lava considerably farther downslope. Even a flow that traveled only several miles could still affect roads, summit facilities, communication infrastructure, or other areas located along its path.
Mauna Kea’s extensive network of older lava flows shows that volcanic activity has repeatedly reshaped the mountain. A future eruption would most likely add another lava flow and potentially another cinder cone to this landscape.
For that reason, the key question would not simply be how far lava could travel. The more important issue would be where the next vent opened and which areas lay downslope from it. Once the vent location and eruption rate were known, scientists could better assess the likely direction and potential reach of the lava flow.
Could Mauna Kea Produce Explosive Eruptions and Ashfall?
Yes. Explosive activity and ashfall are also possible during a future Mauna Kea eruption. The volcano’s geologic record contains extensive tephra deposits produced during past eruptions, showing that Mauna Kea has not always been limited to quiet lava effusion.
Past postshield eruptions produced cinder cones and large amounts of tephra around their vents. Some eruptions were energetic enough to fragment magma and surrounding rock, depositing ash and other volcanic particles across parts of the mountain. The distribution of these deposits shows that explosive activity has played an important role in shaping Mauna Kea’s upper slopes.
The amount of ash produced by a future eruption would depend on the eruption style, magma characteristics, interaction with water or ice, and the intensity of the activity. Larger explosive episodes could send finer particles into the atmosphere, where winds could transport them away from the immediate eruption site.
Not all tephra would travel equally far. Larger volcanic fragments would generally fall closer to the vent, while fine ash could remain airborne longer and be carried farther by the wind. This means that the area affected by significant ashfall would depend not only on the size of the eruption but also on wind direction and speed at different elevations.
Mauna Kea’s high elevation and history of snow and ice add another important factor. Past eruptions occurred when glaciers covered parts of the upper mountain, and interactions between erupting lava and glacial ice produced explosive activity and fine volcanic material. A future eruption occurring when substantial snow or ice was present could therefore produce different effects from an eruption under drier conditions.
The presence of snow or ice would not automatically mean that a future eruption would become highly explosive. The outcome would depend on the location and intensity of the eruption and how magma interacted with water. A future event could range from predominantly lava-producing activity to an eruption that also generated significant tephra and ash.
Ashfall could affect areas beyond the immediate slopes of Mauna Kea, but the extent would be highly variable. Fine ash could be carried downwind and potentially affect roads, vehicles, infrastructure, vegetation, and air quality. However, there is no single distance that can be assigned to a future ash plume because atmospheric conditions could change throughout an eruption.
The greatest concentrations of tephra would generally be expected closer to the eruptive vent. Past Mauna Kea deposits show that tephra can accumulate substantially around individual vents and cinder cones, while finer material can be transported farther away.
For this reason, a future Mauna Kea eruption should not be viewed as exclusively a lava-flow event. Lava would likely be an important hazard, but explosive activity, tephra, and ash could also contribute to the overall impact depending on how the eruption developed.
Could Snow and Ice Make a Mauna Kea Eruption More Dangerous?
Yes, but the effects would depend heavily on how much snow or ice was present when an eruption occurred and where the eruption took place. Mauna Kea is unusual among Hawaiian volcanoes because its summit has experienced repeated glaciation in the past, and snow still accumulates on the mountain during winter. Geologic evidence shows that ice covered parts of the summit during several periods of the Late Pleistocene.
If a future eruption occurred while substantial snow covered the upper mountain, hot lava or other eruptive material could melt some of that snow. The resulting water could interact with loose volcanic material and newly erupted deposits, potentially producing localized runoff, sediment movement, or other water-related effects.
The interaction between volcanic activity and ice could also influence the character of an eruption. Past Mauna Kea eruptions occurred beneath or near glaciers, and some produced unusually fine-grained volcanic deposits. Scientists have suggested that water-rock interactions occurred when lava encountered glacial ice, contributing to explosive ash-producing activity.
This does not mean that every future eruption would become highly explosive simply because snow was present. The amount of available water, the location of the vent, the temperature and composition of the magma, and the thickness of snow or ice would all influence the interaction. A future eruption could still be dominated by lava flows with relatively limited water-related effects.
Snow and ice could also affect the movement of volcanic material after it was deposited. Meltwater flowing downslope could transport loose ash, cinders, and sediment into existing channels and depressions. The scale of this process would depend on how much snow melted and how much loose volcanic material was available.
The summit environment would therefore be particularly important during an eruption. A vent opening beneath or close to substantial snow or ice could produce a different set of hazards from a vent erupting on a snow-free part of the mountain. Scientists would need to evaluate both the volcanic activity and the amount and distribution of frozen water on the mountain.
However, Mauna Kea’s modern snow cover is very different from the thick glaciers that existed there during past ice ages. The largest documented glacial deposits formed during periods when much greater quantities of ice covered the summit. Today, snow is generally seasonal and variable, so the scale of any lava–snow interaction during a future eruption would depend strongly on the season and weather conditions.
For this reason, snow and ice would be an additional factor rather than the primary hazard of a future Mauna Kea eruption. Lava flows would remain the major concern, while explosive activity, ashfall, and localized water and sediment movement could become more important if an eruption interacted with significant snow or ice.
The effects would ultimately depend on where and when the eruption occurred. A summer eruption during relatively snow-free conditions could behave very differently from an eruption at high elevation during a period of substantial snow cover.
Which Areas Could Be Affected by a Mauna Kea Eruption?
The areas affected by a future Mauna Kea eruption would depend primarily on where the new vent opened and which direction lava and volcanic material traveled. Because Mauna Kea has produced eruptions from scattered vents across its summit and upper flanks, the affected area could vary substantially from one eruption to another.
The immediate surroundings of a new vent would face the greatest concentration of volcanic hazards. Lava, falling volcanic fragments, tephra, and gases could affect the upper slopes around the eruption site. A new cinder cone could also develop around the vent, while lava flows could begin moving downslope through the surrounding terrain.
Lava would be particularly important because it would follow the topography rather than spreading equally in every direction. Areas located downslope from the vent would have the greatest potential to be affected by lava flows. Steep slopes could channel lava into particular valleys or drainage areas, while changes in terrain could cause flows to slow, divide, or spread laterally.
The potential affected area would not be limited to the summit. Mauna Kea’s geologic record shows that postshield eruptions produced lava flows extending down the volcano’s flanks, while tephra and ash were deposited beyond individual cinder cones. This means that a future eruption could affect parts of the upper and middle slopes even if the vent itself opened high on the mountain.
Wind would create a different pattern for ash and fine tephra. Unlike lava, which is strongly controlled by the terrain, ash can travel downwind across areas that are not directly downslope from the volcano. The distance and concentration of ashfall would depend on the size of the eruption, particle size, and atmospheric conditions at the time.
The direction of lava movement would also determine whether developed areas and infrastructure were threatened. USGS assessments have noted that a future Mauna Kea eruption could potentially cause serious damage to property and infrastructure, particularly if lava traveled toward the Waimea area or the Hamakua Coast.
However, this does not mean that these areas would necessarily be affected by every future eruption. A vent could open on another part of Mauna Kea and produce lava flows that remain largely confined to different sections of the mountain. The location of the vent would therefore be critical to determining the actual hazard footprint.
The broader island would also not experience the same level of danger everywhere. The greatest lava-flow risk would be concentrated along potential flow paths, while ash and fine volcanic particles could affect a wider area depending on wind direction. This combination means that a future eruption could create a highly uneven pattern of impacts across the landscape.
For communities and infrastructure farther from the volcano, the most important concern would therefore be whether a lava flow reached their area or whether winds carried ash in their direction. Scientists would be able to refine these assessments as an eruption developed by combining the vent location, lava output, terrain, weather conditions, and observations of how the volcanic material was moving.
Could a Mauna Kea Eruption Affect Waimea and the Hamakua Coast?
Yes. Waimea and the Hamakua Coast could potentially be affected by a future Mauna Kea eruption, particularly if a lava flow developed on a part of the volcano that directed it downslope toward these areas. USGS assessments have specifically identified both the Waimea area and the Hamakua Coast as places where a future lava flow could cause significant damage to property and infrastructure.
The possibility is supported by Mauna Kea’s eruptive history. Past eruptions have produced lava flows that traveled considerable distances down the volcano’s flanks. One of the younger flows from Puʻu Kanakaleonui traveled more than 12 miles northeastward before reaching the ocean and helping form Laupahoehoe Point. This demonstrates that lava from high on Mauna Kea can reach far beyond the immediate summit area.
A future eruption would not necessarily send lava toward the Hamakua Coast. The location of the new vent would determine the initial direction of the flow, while the steep and irregular topography of Mauna Kea would influence how the lava moved downslope. A vent on another part of the mountain could instead direct lava toward a different portion of the island.
Waimea could face a different type of exposure because of its location on the western side of Mauna Kea. Whether lava reached the area would depend on where the eruption occurred and whether the flow found a continuous downslope pathway toward developed land. The presence of a vent on Mauna Kea would therefore not automatically place Waimea at risk.
The Hamakua Coast could potentially face a lava-flow pathway from eruptions on the northeastern side of the mountain. Mauna Kea’s northeastern flank contains numerous older lava flows, and the geologic record shows that lava has repeatedly traveled toward the coast in this direction.
The distance a future flow traveled would also depend on the amount of lava erupted. USGS estimates that the longest future flows could travel roughly 9 to 15 miles downslope, although many flows would be shorter. A flow reaching the lower slopes or coastal areas would therefore require a combination of an appropriately located vent, sufficient lava output, and terrain that allowed the lava to continue moving downslope.
Even before reaching populated areas, lava could affect roads, utilities, communications infrastructure, agricultural land, and other property along its path. Once a lava flow reached lower elevations, its impacts could become more significant because more infrastructure and developed land are present there.
Ash and tephra could also affect Waimea or the Hamakua Coast independently of lava. Unlike lava, which is strongly controlled by terrain, fine volcanic particles can be carried by wind. The areas receiving ashfall would therefore depend on atmospheric conditions during the eruption rather than simply their position downslope from the volcano.
However, a future Mauna Kea eruption would not necessarily become a major disaster for these communities. The volcano’s postshield eruptions have generally occurred at low eruption rates, and the exact vent location would be unknown until an eruption actually developed. Scientists would be able to refine the hazard assessment as seismic activity, ground deformation, vent location, lava output, and flow direction became clearer.
The most important point is that Mauna Kea’s hazards would be highly localized by the eruption’s location. Waimea and the Hamakua Coast are possible areas of concern, not areas that would inevitably be covered by lava. A future eruption could produce a flow that remains high on the mountain or moves toward an entirely different part of the volcano.
For this reason, the greatest concern for communities around Mauna Kea would be the development of a lava flow with a pathway toward populated or heavily used areas. The next question is how such an eruption could affect the roads, infrastructure, and facilities located high on the mountain itself.
What Would Happen to Roads, Infrastructure, and the Mauna Kea Summit?
A future Mauna Kea eruption could disrupt roads, communications, scientific facilities, and other infrastructure on the mountain, particularly if a new vent opened near existing summit access routes. The level of disruption would depend heavily on where the eruption occurred and whether lava flows moved toward developed areas. Because Mauna Kea has produced eruptions from different parts of its upper flanks, not every eruption would affect the same infrastructure.
The most immediate concern near an eruptive vent would be the presence of lava and falling volcanic material. Lava could bury roads and access routes if a flow crossed them, while tephra and ash could accumulate on surfaces and interfere with vehicles and equipment. A new cinder cone could also develop around the vent, permanently changing the local landscape.
The summit area would be particularly sensitive because it contains important scientific facilities and is connected to lower elevations by mountain roads. If an eruption occurred nearby, access to the summit could become restricted or temporarily closed because of lava, ash, volcanic gases, unstable terrain, or other hazards. Even if lava did not reach a facility directly, an unsafe approach route could prevent people and equipment from reaching it.
Ash and tephra could create additional problems for infrastructure. Fine particles can accumulate on roads, vehicles, buildings, and mechanical equipment, while reduced visibility could make travel more difficult. The extent of these effects would depend on the amount of material produced and the direction of the wind.
Scientific observations would become especially important during an eruption. Monitoring equipment could help scientists track earthquakes, ground deformation, the position of eruptive vents, and the movement of lava. However, instruments located close to an active vent could themselves become inaccessible or damaged if volcanic material reached the area.
The summit facilities would not all face the same level of danger. A vent opening several miles away could produce little or no direct damage to a particular facility, while a nearby lava flow could completely cut off access. This is another reason why the location of the future vent would be one of the most important factors in determining the practical effects of an eruption.
Infrastructure farther from the mountain could also experience indirect disruption. If major roads or other transportation routes were affected, movement of people and supplies could become more difficult. Ashfall could create additional temporary problems even in areas that were never threatened by lava.
Mauna Kea’s long periods of quiet and relatively low eruption rate allow scientists to monitor the volcano and assess changing conditions if unrest develops. Current monitoring includes seismic instruments and GPS measurements, which can help identify changes before an eruption.
Overall, a Mauna Kea eruption would not necessarily destroy the summit infrastructure, but it could significantly disrupt access and operations depending on the location and behavior of the eruption. Lava flows would pose the greatest direct threat to roads and property, while ash, tephra, gases, and restricted access could create wider operational problems.
The duration of these disruptions would then depend on how long the eruption continued and how quickly lava flows, ashfall, and other hazards declined.
How Long Would the Effects of a Mauna Kea Eruption Last?
The effects of a future Mauna Kea eruption could continue for months or even several years, although the duration would depend on how the eruption developed. USGS assessments of Mauna Kea’s past postshield eruptions suggest that these eruptions probably lasted from months to several years, giving enough time for substantial cinder cones and lava flows to form.
The most intense phase would not necessarily continue for the entire eruption. An eruption could begin with earthquakes and other signs of unrest, followed by the opening of a vent and the production of lava, cinders, and tephra. Activity could then weaken, pause, or change in intensity before eventually ending.
Lava flows could remain an important hazard even after the most explosive activity had declined. As long as lava continued to emerge from a vent, it could accumulate near the source or move downslope through existing terrain. A relatively slow-moving flow could therefore continue creating hazards over an extended period even without a continuously violent eruption.
The effects of ash and tephra would follow a different timeline. Ashfall could occur during individual explosive episodes rather than continuously throughout the entire eruption. Once an ash-producing episode ended, airborne particles would gradually settle, although accumulated ash could continue to create problems for roads, vehicles, equipment, and other infrastructure.
Some impacts could last well beyond the end of the eruption itself. Roads buried by lava would not automatically become usable again once volcanic activity stopped, and infrastructure covered by thick lava or damaged by heat could require extensive reconstruction. Areas affected by loose volcanic deposits could also experience erosion and sediment movement after rainfall.
The landscape changes would be essentially permanent. A new cinder cone, lava flow, or thick tephra deposit would remain as part of Mauna Kea’s geology long after the eruption ended. Over time, weathering and erosion would gradually reshape these deposits, but the volcanic features themselves could remain visible for thousands of years.
The duration of disruption would therefore vary considerably from place to place. An area close to the vent could experience hazards for as long as eruptive activity continued, while a community farther away might experience only temporary ashfall or transportation disruptions. Areas directly covered by lava could face much longer-lasting consequences because the physical landscape and infrastructure would have been permanently altered.
It is also important not to assume that a longer eruption would automatically be more destructive. A relatively low-output eruption lasting several years could produce less immediate damage than a shorter eruption with a large lava output or significant explosive activity. The volume and direction of eruptive material would matter as much as the duration.
Overall, a future Mauna Kea eruption could be a long-lasting volcanic episode rather than a single short event. Past eruptions provide evidence for activity lasting months to years, but scientists would only be able to determine the actual duration and changing hazard pattern as the eruption unfolded.
Even after the eruption ended, its effects could remain visible across Mauna Kea for generations through new lava flows, cinder cones, and altered infrastructure.
Conclusion
A future Mauna Kea eruption could begin as a localized event, but its effects could extend well beyond the immediate summit area depending on where a new vent opened and how much lava and tephra were produced. Mauna Kea’s long period of quiet does not mean that the volcano is extinct; its geologic history shows that it is likely to erupt again.
The most important hazard would probably be lava flows. Past eruptions have produced thick, rubbly lava flows that traveled downslope, and USGS estimates that the longest future flows could potentially reach about 9 to 15 miles. The direction of those flows would depend primarily on the location of the future vent and the terrain surrounding it.
A future eruption could also produce cinder cones, tephra, ashfall, and explosive activity. Snow and ice could further influence an eruption if activity occurred near the summit during periods of substantial snow cover. These hazards would not necessarily affect the same areas at the same time, making the exact eruption scenario difficult to predict in advance.
Communities and infrastructure would face very different levels of risk depending on the eventual lava-flow pathway. Waimea and the Hamakua Coast are among the areas that could potentially experience significant impacts if a future flow traveled in their direction, while other eruptions could remain largely confined to higher elevations.
A future eruption could be preceded by detectable changes in seismicity and ground deformation, allowing scientists to monitor the developing situation and refine hazard assessments as the eruption approached.
Ultimately, Mauna Kea would not necessarily erupt like Kīlauea or Mauna Loa. Its advanced postshield stage, steeper terrain, scattered vents, and history of thick lava flows and cinder cones give it a distinctive eruptive style. If Mauna Kea erupted again, the location of the vent would be the key factor determining what happened next.